Validity of BMI based on self-reported weight and height in adolescents

Aim: To assess in a subset of a nationally representative sample of Portuguese adolescents, the validity of Body Mass Index (BMI) based on self-reported weight and height. Methods: This study included 462 students in grades 6, 8 and 10 (mean age 14.0 +/- 1.9 years) from 12 public schools randomly selected from the list of schools which took part in the 2006 Health Behaviour in School Aged Children Portuguese survey, corresponding to approximately 10% of the sample. Self-reported weight and height were recorded and then measured. Results: Prevalence of normal weight, overweight and obesity based on self-report compared with that of measured values was not significantly different for boys and girls, and among age groups. BMI based on measured weight and height was underestimated compared with BMI based on self-reported data, both among girls and boys. Larger limits of agreement were found for boys, indicating a higher variability of self-reported BMI in estimating measured BMI, specifically below the age of 14 years. Conclusion: These data suggest that BMI based on self-reported weight and height is not accurate for BMI prediction at an individual level. However, self-reported BMI may be used as a simple and valid tool for BMI estimates of overweight and obesity in epidemiological studies.